1. Field of the Invention
The present invention relates to a numerical control system having a numerical controller connected via communication to a motor driving amplifier which drives a motor included in a machine, the device having a motor control unit controlling the motor mounted therein.
2. Description of the Related Art
In a numerical controller, for example, as disclosed in Japanese Patent Application Laid-Open No. 9-69004, functions of a numerical control unit, a motor control unit, a PMC (programmable machine controller) unit, and others are connected to each other via a bus. FIG. 6 is a diagram depicting a schematic structure of a numerical controller using a conventional technology. In general, as a motor control processor for use in a motor control unit, a low-price DSP (digital signal processor) is often used.
In the structure in which a motor driving amplifier is connected via communication and motor control processors are collectively mounted on a numerical controller, the number of control axes for each motor control processor has an upper limit, and therefore the number of motor control processors has to be increased as the number of control axes in the numerical controller is increased. This is because the number of axes of the numerical controller varies depending on the machine tool to be controlled.
If a low-price DSP is used as a motor control processor for the motor control unit, it is convenient to easily adjust the number of processors according to the number of control axes. However, the low-price DSP is generally connected to an external resource via a general-purpose parallel bus and thus cannot be directly connected to a local bus. Therefore, a bus bridge is required. For this reason, the number of connection pins is increased. With an increase in the number of low-price DSPs, the number of LSIs of the bus bridge also has to be increased, restricting the number of mountable DSPs. Moreover, an increase of the number of control axes is adjusted with the number of DSPs, and therefore a small-sized DSP with low power consumption has to be selected.
As described above, in the method of using low-price DSPs as motor control processors to increase the number of motor control processors, that is, low-price DSPs, for use to enhance scalability of the numerical controller, it has been difficult to address the need in recent years for making a machine tool multi-axial and high-functional. This is because the number of mountable processors has a limit and it has been extremely difficult to increase operating frequency in recent semiconductor technology. It is also difficult to increase the number of control axes per processor.